A majority of Superfund sites are contaminated with dense non-aqueous phase liquids (DNPLs), which typically have health based cleanup levels for concentrations in the aqueous phase that are several orders of magnitude less than the aqueous solubility of such solutes. The remediation of sites contaminated with DNAPLs has been found to be perhaps the most difficult problem facing Superfund cleanup efforts. The overall goal of this project is to develop improved methods for quantifying and remediating DNAPL-contaminated porous medium systems, which do not suffer from limitations associated with standard methods. This overall goal can be divided into the following specific aims: (1) to investigate the mechanisms and extent of density-motivated DNAPL mobilization in two-fluid-phase, heterogeneous porous media systems; (2) to analyze the range of applicability and accuracy of partitioning tracer methods for the measurement of DNAPL volumes presented in heterogeneous systems; (3) to evaluate approaches for removing DNAPL residual after density-motivated displacement of DNAPLs has been performed; (4) to investigate the mechanisms and extent of density-motivated DNAPL mobilization in three-fluid-phase, heterogeneous porous media systems; (5) to evaluate the effects of geochemical conditions on density-motivated remediation methods; (6) to develop and apply a high-resolution numerical model to design, describe, and predict results, from laboratory experiments of density-motivated remediation; and (7) to use the numerical model to simulate a wide range of conditions representative of typical heterogeneous field-scale conditions. Two basic conceptual approaches will be used in this work. In the first approach, the resident aqueous phase will be displaced by a dense brine solution, such that this DNAPL become less dense than the brine solution and is motivated by buoyancy forces to move upward toward the unsaturated zone. Because the DNAPL is typically the non-wetting phase compared to both the original aqueous phase and the brine, it will tend to occupancy the largest pore openings under both the emplacement and mobilization phases. The second basic approach is to float a layer of brine between an impermeable layer and a DNAPL contaminated region and then remove the fresh water from the DNAPL contaminated region, leaving the DNAPL-contaminated region unsaturated. This approaches results in DNAPL being an intermediate wetting phase in most cases and a significant increase in gravity forces, which will result in a relatively high and rapid rat of DNAPL removal down to the brine layer. The brine layer will be controlled and used to capture the DNAPL.